The present application claims priority under 35 U.S.C xc2xa7 119 based upon Swiss Patent Application No. 2000 1768/00 filed on Sep. 12, 2000.
The invention concerns a method and an apparatus for mounting semiconductor chips.
With the mounting of semiconductor chips, the substrate is fed by a transport arrangement in cycles to a dispensing station where adhesive is applied and then to a bonding station where the next semiconductor chip is placed. With increasing miniaturisation of the electronic structures, the semiconductor chips for certain applications also become very small. The dimensions of the smallest semiconductor chips already amount to less than 0.2 mm*0.2 mm. If the adhesive layer between the substrate and the semiconductor chip consists of an electrically conducting adhesive, the task is set of mounting the tiny semiconductor chips so that, after hardening, the thickness of the adhesive layer between the substrate and the semiconductor chip is uniform and only varies within tight given tolerances for example of only xc2x15 xcexcm. Only in this way can a consistently high quality of the electrical characteristics of the mounted semiconductor chips be achieved. Furthermore, it is demanded that substrate from different manufacturers can be used which means that the thickness of the substrate to be processed is subject to deviations of typically 60 to 70 xcexcm.
Today, a method generally known as xe2x80x9covertravelxe2x80x9d is used to compensate the thickness variations of the substrate. The automatic assembly machine, a so-called die bonder, comprises a bondhead with a pick-up tool to pick up the semiconductor chip. The bondhead is lowered to a predetermined height above the substrate which is set so that, in any case, the semiconductor chip impacts on the adhesive portion regardless of the actual thickness of the substrate. In doing so, on the one hand the adhesive is compressed and, on the other hand, the pick-up tool is deflected in relation to the bondhead. The thickness of the resulting adhesive layer is subject to large variations.
The object of the invention is to propose a method and an apparatus for the mounting of semiconductor chips which fulfils the above-mentioned requirements.
Solving of the task is achieved with a method by which the semiconductor chip is deposited on the adhesive portion under controlled conditions. Decisive for achieving an adhesive layer with negligible thickness variations is that the impact of the semiconductor chip on the adhesive portion is considerably reduced in comparison with prior art. This is achieved in that it is not the semiconductor chip and the entire bondhead which impact on the adhesive but only the semiconductor chip and a small part of the bondhead, namely the pick-up tool at the tip of which the semiconductor chip is located.
With the mounting of a semiconductor chip onto a substrate having a portion of adhesive the bondhead is therefore lowered to a predetermined height H above a support holding the substrate where as a rule the semiconductor chip does not yet touch the adhesive or only just touches so that the portion of adhesive is only negligibly deformed. At the same time, the pick-up tool is fixed in an upper limit position on the bondhead. As soon as the bondhead has reached the height H, the fixing of the pick-up tool is released so that the pick-up tool moves downwards from the upper limit position and presses the semiconductor chip onto the adhesive. After a predetermined time after releasing the fixing of the pick-up tool, the bondhead is raised and moved away.
With a bondhead particularly suited for the method, the pickup tool and the bondhead are connected by means of a chamber to which compressed air and/or vacuum can be applied so that, to a large extent, the movement of the pick-up tool can be controlled.
The method according to the invention and the embodiments of apparatus suitable for carrying out the method are now explained in more detail based on the drawing.